Causes of mass extinction of sea organisms at the Paleozoic-Mesozoic boundary

Abstract

At the end of the Permian, at the Paleozoic-Mesozoic boundary (251.0 ± 0.4 Ma ago), 96% of oceanic organisms became extinct. The extinction lasted three million years, but the most intense and abrupt event was 251.4 Ma ago. A series of more or less substantiated hypotheses was suggested to explain this catastrophe: anoxia, higher CO2 and H2S contents, fall of the sea level, volcanism, and impact events confirmed by several impact craters. The synchronous variation in many factors responsible for biodiversity reduction, including those without casual relations, proves the existence of a common cause of primarily cosmic origin.

Full text

ISSN 1028334X, Doklady Earth Sciences, 2011, Vol. 438, Part 2, pp. 750–753. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © M.S. Barash, 2011, published in Doklady Akademii Nauk, 2011, Vol. 438, No. 6, pp. 777–781.
750
At the end of the Permian, at the Paleozoic–Meso
zoic boundary (251.0
±
0.4 Ma ago), 96% of the oce
anic organisms became extinct. This was the greatest
mass biota extinction in the Earth’s history. The biodi
versity in the Late Permian included about 250 000 spe
cies, whereas after the disaster it decreased to less than
10 000. The bottom of the Permian–Triassic Panta
lassa Superocean, which occupied 2/3 of the Earth’s
surface, was nearly completely subducted. The frag
ments of the midoceanic rocks remained as accre
tionary blocks near the active continental margins.
The sediments of marginal seas are found in many
regions of the modern continents. The midoceanic
sediments deposited at the Permian–Triassic bound
ary include shallow carbonates of paleoatolls and
cherts as deep sediments. The study of the distribution
of paleontological objects shows that both the biota
extinction and global changes in environmental con
ditions occurred during two phases: (1) at the Middle–
Late Permian boundary (260 Ma ago) and (2) at the
Permian–Triassic boundary (about 251 Ma ago).
In the first phase, the amount of genera reduced at
the expense of the benthos (rugose corals, fusulinids,
brachiopods, bryozoans, echinoderms, etc.), which is
explained by anoxia. During the second phase, low
oxygen or anoxic conditions covered the entire water
column in the ocean (superanoxia). The biodiversity
was mainly reduced at the expense of nekton and
plankton (ostrakods, radiolarian, etc.). The global col
lapse of bioproductivity is considered to be the cause
of the mass extinction of radiolarians, the most impor
tant plankton species. The complete extinction of the
major benthic forms—fusulinids and rugose corals—
may have been governed by the extinction of symbiotic
algae which, in turn, was probably caused by insola
tion reduction. Ammonoids and nautiloids and
other predators (fishes and conodonts) were sub
jected a little.
The organism extinction at the Permian–Triassic
boundary was studied in detail in Meishan Province,
South China. Figure 1 demonstrates statistical analy
sis of the distribution of sea organisms. The extinction
lasted three million years, but the most intense and
abrupt event in an interval of less than 500 years
occurred 251.4 Ma ago. This coincides with a sharp
decrease in
δ
13
С
carb
and an increase of ~100 times in
the amount of volcanic microspherules. Pyrite inter
layers (evidence of anoxia) and volcanic ash are
observed at this boundary. The Ir content was found to
be an order higher than its background concentration
in the Upper Permian and Lower Triassic sediments
[12]. Finally, a fast transgression occurred that time
and a new cosmopolitan conodont species
H. parvus
appeared.
Many hypotheses were suggested in order to
explain the extinction of organisms: disappearance of
ecological niches during the continental amalgam
ation into Pangea; hypersalinity; anoxia; higher CO
2
and H
2
S contents; fall of the sea level down to the min
imal value in the Phanerozoic; transgressions; volcan
ism; warming and acid rains as a result of volcanism
and methane release from gas hydrates; and a short
term fall in temperature. All these factors which
reduced the biodiversity are substantiated by paleon
tological, geological, geochemical, isotopic, and other
data. Some factors yield visible relations but other
relations are absent or unknown.
Causes of Mass Extinction of Sea Organisms
at the Paleozoic–Mesozoic Boundary
M. S. Barash
Presented by Academician A.P. Lisitsyn January 24, 2011
Received January 24, 2011
Abstract
—At the end of the Permian, at the Paleozoic–Mesozoic boundary (251.0
±
0.4 Ma ago), 96% of
oceanic organisms became extinct. The extinction lasted three million years, but the most intense and abrupt
event was 251.4 Ma ago. A series of more or less substantiated hypotheses was suggested to explain this catas
trophe: anoxia, higher CO
2
and H
2
S contents, fall of the sea level, volcanism, and impact events confirmed
by several impact craters. The synchronous variation in many factors responsible for biodiversity reduction,
including those without casual relations, proves the existence of a common cause of primarily cosmic origin.
DOI:
10.1134/S1028334X11060286
Shirshov Institute of Oceanology, Russian Academy
of Sciences, Nakhimovskii pr. 36, Moscow, 117997 Russia
GEOLOGY

DOKLADY EARTH SCIENCES Vol. 438 Part 2 2011
CAUSES OF MASS EXTINCTION OF SEA ORGANISMS 751
Why were the processes active in such a restricted
period of the geological scale so different and harmful
for the biota? Did asteroid impacts play any significant
role as occurred 65 Ma ago, at the Mesozoic–Ceno
zoic boundary?
The above factors did occur at the end of the Per
mian over about eight million years. The variations in
the internal geospheres and the Earth’s surface and
biosphere took place simultaneously. The relation of
biodiversity with tectonics, geoid evolution, mantle
convection, and even the nucleus shift that caused
geopolar change is suggested. The casual relations
were accomplished through the fluctuation in sea
level, volcanism, methane release, intensification of
the ocean stratification, anoxia, etc. (Fig. 2).
The variations in the ratio of some isotopes reflect
the deep changes in ecology at the Permian–Triassic
boundary. The
δ
13
C
ranged from +5–7 to –2–4
‰
,
which proves a sharp variation in bioproductivity. The
decrease in the
87
Sr/
86
Sr
value down to the Phanero
zoic minimum is explained by the change in weather
ing in the course of land aridization. The drastic
decrease in
δ
18
O
is related to warming. The shift of
δ
34
S
values is explained by the bacterial sulfatereduc
tion of
32
S
during pyrite burial and the formation of
framboidal pyrite under strong euxinic conditions [11].
In the Phanerozoic, the Mg/Ca ratio in seawater
varied from 1.0 to 5.2, which is caused by the mixing of
the midoceanic hydrothermal and river waters. The
Mg/Ca ratio of seawater fluctuates inversely to the
global speed of the oceanic crust growth [10]. The
period from the end of the Paleozoic to the beginning
of the Mesozoic is an interval of mostly aragonite sed
imentation, so the global rifting rate was minimal,
which corresponds to the integration of Pangea.
By the modern views [7], the variations in different
systems of the Earth began about 265 Ma ago when the
Illavara polarity change occurred after the 50 Ma sta
bility of the geomagnetic field that provoked the fre
quent changes in the geomagnetic field over a long
time. This event which was caused by the changes in
the Earth’s core and mantle condition was shown on
the Earth’s surface five million years later in the series
of events mentioned above.
At the end of the Permian, the sea level fell down to
the Phanerozoic minimum that is related to the inte
gration of Pangea, and, first of all, the shelf communi
ties suffered. The shortterm fall of temperature was
probably contemporary with this event.
The changes in the climatic system took place at
the end of the Permian and beginning of the Triassic
[9]. The Hercynian Orogeny gradually stopped, which
decreased the chemical weathering of silicates and,
consequently, the supply of biogenic components into
the biosphere, which decreased more with warming.
The pole–equator thermal gradient weakened,
0-224
250
251
252
253
TriassicPermian
Ma
δ
13
С, ‰
(PDB)
Species
Fig. 1.
Stratigraphic distribution of species in the section of the Meishan Province and variation in
δ
13
С
, simplified after [8].

752
DOKLADY EARTH SCIENCES Vol. 438 Part 2 2011
BARASH
upwellings decreased, and productivity and carbonate
precipitation decreased. After the completion of the
submergence of subpolar water, the ocean was quickly
filled with warm, low oxygen water. The transgression
has bought the anoxic condition in the shelf areas,
which was a cause of the mass extinction proved for the
end of the Permian by facial, geochemical, and biom
arker studies.
The large scale midoceanic and intraplate basaltic
volcanism is the most popular hypothesis of the Late
Permian extinction. The temporal coincidence
between basaltic eruptions in South China and the first
phase of biota extinction 260 Ma ago and also between
the giant eruptions of the Siberian traps and the main
extinction phase was traced. Acid and intermediate
volcanism was widely developed along the western
boundary of the Pantalassa Superocean. In South
China alone, the volcanoclastic layer covers a territory
of more than 1 million km
2
. Eruptive volcanism gener
ated huge masses of gases and ash, occurred at the
areas of carbonate sediments, and brought about the
great release of CH
4
and CO
2
volumes enlarging the
effect of the Siberian traps.
The eruption brought on the “volcanic winter”
accompanied with a global fall in temperature because
of the aerosol screening in the atmosphere, gas release,
and acid rains harmful for plants. After the main basal
tic eruption, the following “volcanic summer” hin
dered the recovery of biodiversity and heightened the
ocean stratification. The gas hydrate decomposition
led to the release of a huge amounts of CO
2
and onset
of a strong and disastrous greenhouse effect. The fast
global warming led to weakening of the upwellings,
ocean stagnation, and decrease in productivity.
Although the reviewed factors negatively influenced
the biodiversity, they developed slowly and did not
cause rapid mass organism extinction on a global
scale.
The impacts of large asteroids or comets could also
be responsible for the sharp variations in ecological
conditions. Evidence of impact events were found at
the Permian–Triassic boundary in several sections.
However, the real craters were discovered only in
recent years, such as, for example, the Bedout astrob
leme (18.18° S, 119.25° E) covered with sediments
and located in northwestern Australia, 25 km from the
coast [3]. It was studied with seismography and
gravimetry and was drilled by two wells down to 3000 m
deep. The central part of the crater 180–200 km across
with Ar/Ar ages of 250.1 ± 4.5 and 253 ± 5 Ma is char
acterized by an uplift as in the Chixulub Crater.
Other craters formed at the Permian—Triassic
boundary are also known [4]. The largest in the South
America, the Araguainha Crater (16.77° S, 52.98° W,
40 km across), was found in Brazil. The fall of an aster
oid 2–3 km in diameter took place about 250 Ma ago.
The Arganaty Crater in Kazakhstan (49.5° N, 67° E,
315 km across, 250 Ma) is also a reliable crater. The
Falkland Crater (51° S, 60° W, 300 km across, 250 Ma)
is a probable astrobleme. The following craters are less
trustworthy: Great Kuonamki in the East Siberian
Platform (70° N, 111° E, diameter is not indicated,
251 Ma), Guli (70.91° N, 101.2° E, >50 km across,
251 Ma), Essey (68.81° N, 102.18° E, 4.5 km across,
Fig. 2.
Relation between abiotic factors and mass extinction of organisms at the Permian–Triassic boundary, modified after [13].
Sea level is shown after [6].
δ
13
С, ‰
Interaction
Plate
movement
Geoid
Geomagnetic
polarity
Volcanism
Ma
Stratigraphy
TriassicPermian
T
2
T
1
P
3
P
2
240
250
260
270
Integration of Pangea
transitional
level
System of Earth’s surface
Sea
0100
m
−
20 2 4
chemistry
Ocean
Climate Space
Biodiversity
Extinction,
phase 2
Extinction,
phase 1
Impact
craters
Methane
release
Evaporites
Meso
Paleo
Aragonite
and
Anoxia
δ
34
S
Siberian
traps
Chinese
basalts
+
−
+
−−
+
zoic
zoic
Permian–Triassic
mixed superchron
Triassic
−
Jurassic
variable
Carboni
Permian
inverse
ferous
−
Mg/Ca
Evaporites
of internal geospheres

DOKLADY EARTH SCIENCES Vol. 438 Part 2 2011
CAUSES OF MASS EXTINCTION OF SEA ORGANISMS 753
251 Ma), Alpine in Europe (43° N, 8° E, ~250 Ma),
and SAR 28 in Canada (56.57° N, 110.57° W, ~250 Ma,
7.5 km across).
Numerous fragments of chondritic meteorites with
typical geochemical features, impact quartz, metallic
grains, and cosmic fullerenes with incorporated
3
He
were found at the Permian–Triassic boundary layer in
the Antarctic, in the Graphitic Peak of the Central
Transantarctic Mountains [2]. Probably, Wilkes Land
in the Antarctic contains a trace of the impact of the
largest meteorite in the Earth’s history [5]. The large
negative magnetic anomaly coinciding with a ring
depression 243 km wide, 848 m minimal depth, and a
center at 70° S, 120° E was found here. The NASA
subsurface radar mapping revealed a 500km crater
located beneath the EastAntarctic ice shield. It is
considered to be the impact trace of a 55km asteroid
exceeding 4–5 times the Chixulub Asteroid, which led
to the mass extinction of organism 65 Ma ago. Based
on geophysical data, this took place about 250 Ma ago.
Most likely, precisely this event, along with the large
Bedout and other events, was the most important
cause of the drastic mass extinction of organisms at the
Permian–Triassic boundary. Geological samples
under the Antarctic ice have not yet been obtained and
the astrobleme is needed to be proved.
The impacts of large asteroids, especially occurring
within a narrow temporal interval, should exert the
destructive influence on sea and land organisms [1].
They should include a decrease in daylight and varia
tion in temperatures, acid rains, and fires. The global
distribution of the dust clouds composed of cosmic
particles and particles of the Earth’s crust ejected from
the crater would reduce photosynthesis and violate the
entire food chain. The effect could be intensified by
fires. If the asteroid fell in the ocean, then steam rejec
tion may have caused the greenhouse effect. An aster
oid impact on carbonate rocks with high CaCO
3
and
CaSO
4
content would have increased the concentra
tion of C
O
2
and sulfuric aerosols in the atmosphere,
which would have brought acid precipitates and
increase in temperature by several degrees.
Because the relation of extinction at the Creta
ceous–Paleogene and Permian–Triassic boundaries
accompanied by the largest basaltic eruptions and
their synchronism with other harmful factors do not
cause doubts, it is suggested that the impact event
destroyed an already weakened biota. The simulta
neous variation in many factors determinative for
biodiversity, including those without any casual rela
tions, proves the existence of the common primary
cosmic cause.
The age estimation of the impact craters correlates
with the events of the mass organism extinction. In
order to explain the quasiperiodicity of both pro
cesses (about thirty million years), it is suggested to
examine the following cosmic events of similar fre
quency: crossing by the Solar system comet clouds of
the galactic arms, the vertical movements of the Sun
relative to the galactic plane, and the variation in the
gravitation potential of the Galaxy at various distances
from its center. As for the mass extinction of organ
isms, considering their suddenness and shorttime
interval, it may be explained only by the rapid cata
strophic changes in the environmental conditions
caused by asteroid impacts.
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